Executable computer programs include branch instructions that when executed direct program control to target addresses in the program. In some cases, branch instructions are used to transfer control to a code segment that implements a source-code defined function. For example, if the source code sets forth a “function” that averages an input list of values, the function may be invoked by name as needed in the source code. The executable code includes a target code segment that implements the function and branch instructions having target addresses that reference the target code segment. It will be appreciated that different languages have different names for functions such as procedure, routine, or method.
Advances in memory addressing by processors have accompanied the advances in processor speed. A recent milestone is the introduction of the 64-bit processor, which allows computer programs to address 64 bits of address space. However, in some architectures a direct branch instruction has an effective target address range that is less than the total address supported address space. For example, the limit of an instruction pointer relative branch target address is 25 bits in Hewlett Packard Company's 64-bit machines. However, an executable program may occupy an address space that is greater than is addressable with 25 bits. Thus, the address of a branch instruction and the target of the branch instruction may be further apart than is addressable with 25 bits.
Instruction pointer relative branch instructions are referred to herein as “direct branch instructions” or “direct branches.” Direct branches are typically the fastest branch instructions on microprocessors since paths can be predicted well in advance by the hardware, resulting in fast execution times.
An address-bridging code segment is used to bridge the addressing distance between a direct branch and the target code segment if the target code segment is beyond the addressing limit of a direct branch instruction. The way the address-bridging technique works is as follows. When a linker detects that the target code segment of a direct branch instruction is beyond the addressing limit, the target address of the direct branch instruction is modified to reference an address-bridging code segment. The address-bridging code segment is within the direct branch addressing limit and uses an indirect branch to transfer control to the target code segment. An indirect branch instruction allows transfer of control within the full 64-bit address space. On Hewlett Packard's 64-bit machines, “long branch” instructions can be used for the same purpose.
Address-bridging code segments may hinder performance for some applications or libraries. Since the address-bridging code is, from a logic standpoint, unnecessary to provide the functionality of the application, execution of the address-bridging code wastes processor time.
A method and apparatus that address the aforementioned problems, as well as other related problems, are therefore desirable.